The Decapolis serves as a starting point for Aelius Gallus' ill-starred expedition in 25-24 BCE in search of Arabia Felix.

Aelius Gallus, the second praefect of Roman Egypt (Aegyptus) in the reign of Augustus during the years 26–24 BCE, had replaced Cornelius Gallus—with whom he has often been confounded.

Aelius Gallus is also known to be an intimate friend of the Greek geographer Strabo of Pontus and has been identified with the Aelius Gallus frequently quoted by Galen, whose remedies are stated to have been used with success in his Arabian expedition.

Gallus has undertaken the expedition from Egypt by the command of Augustus, partly with a view to explore the country and its inhabitants, and partly to conclude treaties of friendship with the people, or to subdue them if they should oppose the Romans, for it is believed at this time that Arabia is full of all kinds of treasures.

When Aelius Gallus sets out with his army, he trusts to the guidance of a Nabataean called Syllaeus, who deceives and misleads him.

A long account of this interesting expedition through the desert is given by Strabo—who derives most of his information about Arabia from his friend Aelius Gallus.